Someone explain to me how you can release a movie in 3D that wasn't filmed in 3D originally? The only thing they can do is re-do the CGI in 3D. In which case, that makes the movie partially 3D. Misleading if you ask me.
Same applies to the StarWars Prequel 3D release.
Oh, you can do it. It's not easy, and it's not quick,
especially if you want it to look half-way decent.
The actual process is more than a little technical and involved (and I'm skipping over a lot, if anyone wants to cover anything I omit or gloss over), but in a nutshell, you take each frame of the movie and offset everything in it appropriately to simulate the parallax as if there had been a second camera shooting it, so your original movie is, say, the left eye, and the modified frames are the right eye.
As far as how you actually do this, it's more or less a combination of two techniques (or, if you're in a hurry, it's one of two techniques). One way is to project the original frame onto a 3D plane, and then distort it, like a rubber sheet, pulling parts closer to the camera and pushing other parts farther away. Then you move a virtual camera to the position of the second eye, and that's that. This is good for subtle gradations in depth, like making the tip of someone's nose stick out from the base of their nose, which sticks out from their cheeks, but it falls down when there's a larger gap, like person standing with a wall twenty feet behind them. There's no division between the person and the wall, in that case, so it just looks like a lumpy photo instead of two distinct objects.
The other basic approach has the opposite problem. In this one, you slice each object out of the scene and then arrange them in 3D space, like a shoebox diorama made of cardboard cutouts. You have to paint in anything that you can see from the second eye that had previously been blocked by something in front of it, as well, but that's what gives it the greater sense of separation. The drawback is the loss of subtle depth, giving the appearance that everything in the scene is just a flat card with an actor or prop painted on it.
When combined, these basic techniques get you something that almost kind of looks like a filmed 3D image. Maybe.
Also, for a movie of
Titanic's age, it may not even be possible to render a second-eye perspective of CGI shots. Between operating system and program upgrades, hardware changes, and the sad truth that data archiving is known to suck on occasion, they may not have the old files, may not be able to get them into a modern computer if they do, or may not be able to use them with modern programs if they can.
